Call for Proposals for Altair LGS System Verification

This letter is a Call for Proposals for System Verification (SV)
proposals to use the Altair Laser Guide Star (LGS) system. Two
nights will be available for LGS+NIRI and two nights will be available
for LGS+NIFS. The deadline for proposal submission is June 16,
2006. The Altair Laser Guide Star (LGS) system is currently
undergoing science commissioning at Gemini North Observatory. LGS
will provide users with high angular resolution for science targets
within 25 arcseconds of faint (R ~ 18) guide stars. This represents a
roughly factor 15 reduction in flux requirements over the Natural
Guide Star (NGS) system which has been in place at Gemini since
semester 2004A. The LGS system can be used to feed either NIRI (for
imaging or longslit spectroscopy) or NIFS (for IFU spectroscopy).
Please see the Altair LGS page
for a brief overview of the LGS concept.

The technical commissioning of LGS was completed on April 18, 2006
when all correction loops were closed simultaneously and light was
delivered to NIRI in a mode typical of science use. We are still
conducting the science commissioning of LGS, which involves
characterization and optimization of the correction and streamlining
of the nighttime operations. At this time, we are pleased to invite
the Gemini community to propose System Verification (SV) programs for
LGS. We anticipate 2 nights of SV time for LGS+NIRI and 2 nights of
SV time for LGS+NIFS will be available for SV. Observations are
planned to start in August, 2006 and will be integrated into the
Gemini Queue for execution. LGS will only be planned for CC=50
conditions, although propagation and observation execution is possible
in the thinnest CC=70 conditions. Note that we currently plan to
issue a separate call near the end of July for Demo Science (DS)
observations, for which about 9 nights will be allocated. See below
for the differences between SV and DS.

Initial images from the LGS+NIRI commissioning are
presented here:

NIRI/LGS f/14 image of the Eagle Nebula. This image was obtained
in typical LGS mode, with a single tip/tilt star (slightly above
and to the left of center). Field of view is about 40 arcsec per
side (click image for full size).

NIRI/LGS f/14 image of M13. This image was collected with several
different pointings, each using a different tip/tilt star
centrally located. Field of view is about 100 arcsec horizontal
(click image for full size).

Note that both of the above images were collected prior to image
optimization. We expect to be able to improve the point spread
function and Strehl ratios substantially from the above images during
further commissioning. The images were collected to illustrate the
two major modes of LGS operation as well as highlight the fairly low
anisoplanatism seen with the LGS system. See the Hot News page for the most up-to-date
information.

System Verification is the final step of testing prior to general
use of the instrument by the Gemini community. It is intended to
verify the readiness of the entire system from observation definition
to data reduction. It is also intended to exercise the various modes
of an instrument and demonstrate to the community, through interesting
and challenging science programs. Collaborations for LGS SV projects
within the Gemini partner countries are highly encouraged as we have a
limited number of observing nights and cannot do a large number of
projects. Please circulate this call within your community.

The purpose of SV time is nominally to test the system in modes
typically used for science as well as provide additional data to the
LGS team to estimate performance under a wide variety of observing
modes. In particular, we wish to probe as many aspects of LGS
tip/tilt star brightnesses and separations as possible to begin to
build a database of correction performance versus guide star
selection. Note that an additional ~9 nights of Demo Science (DS) will
be made available in September to a few programs. A separate DS call
will be made in late July for these nights. Demo Science will be
designed to produce a database of interest to the larger scientific
community with a small proprietary period.

The following summary is extracted from the Gemini SV web page:
"SV observations will be selected by SV team members and
approved by the Gemini Director. They will span a wide range
of targets and perspectives and the SV teams will be
responsible for providing written, in depth assessments of SV
observations and mode verification within three months of data acquisition. The data obtained during SV will be made
available by ftp to the international Gemini community and the
assessments will be published on the Gemini SV web
pages. Community participation in the further evaluation and
assessment of the SV observations will help ensure that Gemini
is a success from the first date of scheduled
observations."
Full details are available of the SV process.

Performance: We estimate that the following tip/tilt star
limits will most likely hold to about 1/2 a magnitude, and the Strehl
performance will likely not change by more than a factor 2. High
Strehl Correction in H, K and L (1.6 to 2.5 microns) requires a
bright (8.5 < R < 15) tip/tilt star within 15 arcseconds of the
science target. Delivered Strehls should be about 75% of that seen
for NGS: 20% in H and up to 35% in K. L-band LGS has not been tested.
The background in L will be considerably higher with Altair in the
beam. We believe that some signal-to-noise improvement is likely at L
and angular resolution will be close to the diffraction limit.
Observations shortward of H (such as z and J) should not be considered
High Strehl even for bright tip/tilt stars.
Low Strehl Correction will occur with a faint (15 < R < 18)
tip/tilt star within 25 arcseconds of the science target. Delivered
Strehls should be a few percent in J, up to 10% in H and K. The 25
arcsecond limit is a hard limit based on the Altair optics, i.e. guide
stars further than this cannot be observed with LGS. All
observations shortward of H (1.6 microns) should be considered Low
Strehl. Note that if your Guide Star is brighter than R < 8.5, you
should use NGS instead of LGS due to the danger of damaging the
tip/tilt wavefront sensor.

Both high-Strehl and low-Strehl correction should be possible for
any combination of non-sidereal and sidereal science targets and
tip/tilt stars. Note that galaxies with stellar-like cores may also
be used for guiding. We have no data on which cores could work and
which could fail at this point, however we do not expect guiding to
work if the full width at half-maximum of the core is larger than
about 1 arcsec. (This corresponds to about a 1.5 magnitude drop in
surface brightness per arcsec of distance from the core.)

Altair/LGS is formally a very high performance guider, and thus its
observing modes are primarily due to the science instrument. There are
two basic SV Instrument Modes with LGS:

LGS+NIRI Imaging and Spectroscopy:

LGS+NIRI Imaging
is available at J, H or K with f/14 and at J, H, K or L with
f/32. LGS+NIRI Spectroscopy can be performed in J, H or K at f/32
only.

LGS+NIFS IFU Spectroscopy:

LGS+NIFS IFU Spectroscopy
is available in the z, J, H and K band.

See the NIRI or NIFS webpages for more detailed
science instrument information. To compute exposure times and
sensitivity, use the NIRI+Altair or NIFS Integration Time Calculators
(ITCs) with the following modifications: (1) all LGS observations are
conducted with the Field Lens, so divide the effective guide star
separation by 4 before input into the ITC and (2) all LGS observations
should increase the effective brightness of the tip/tilt star by 3
magnitudes. Thus, if using a 15 arcsec separation R = 14 magnitude
star, one would input 3.75 arcsec separation and R = 11 into the ITC,
yielding a 33% Strehl in the K-band. If using a 25 arcsec separation
R = 18 magnitude star (the current limit of our correction ability),
one would input 7.5 arcsec separation and R = 15, giving a 11% Strehl
in the K-band. To compute observing overheads, add 5 minutes
of extra setup per pointing (a pointing is defined as a unique
tip/tilt star). Note that dithers using the same tip/tilt star do not
require a separate setup, but will incur an additional ~5 seconds per
dither position above NGS overheads. This number may be reduced as we
optimize the system. Note that the Phase I Tool (PIT) does not have
the latest LGS information, so you should manually select your guide
star based in its R-band magnitude and distance.

To submit a program, you must use the 2006B Phase I Tool and
include observing constraints, target lists, and instrument
configuration information. Submit the program through the Phase I
tool interface by June 16, 2006 for full consideration. Before
submitting, select the button labeled "Demo Science or SV" in the PIT
and enter the time requested; do not submit LGS SV proposals to any
other Gemini partner.

Scientific justifications should be brief and clearly state which modes are
being tested. Technical justifications should be complete enough that
feasibility can be assessed easily. In particular, guide star
brightnesses and separations must be included.

PIs seeking SV time will be informed of the results of the selection
process by July 10, 2006, and Phase II files (using the Observing Tool)
for selected programs will need to be completed by July 24.

Disclaimer: Submitting an SV program or even having a SV program selected
as high priority does not guarantee that data will be taken. Selection for
SV will also be based on the abilities of the proposers to reduce the data
and return feedback within a reasonable time. The proprietary period for
SV data is three months. At the end of the 3 month period, PIs and their
collaborators will need to provide reduced data for public release.

Please feel free to contact us with questions or comments - we look
forward to hearing from you and reading your LGS SV proposals.